1. Field of the Invention
This invention relates to wireless communication systems and in particular to a method for a plurality of backhaul communication signals to concurrently use the same backhaul channel during transmissions between repeaters and a base station.
2. Description of Relevant Art
Many phone networks, including cellular phone networks, operate as circuit-switched networks. Circuit-switched refers to a type of network in which a particular physical path, commonly referred to as a data path, is obtained for and dedicated to each connection between two end-points in the network. The particular data path used for the connection is dedicated for exclusive use by the network endpoints during the entire duration of the connection. Thus, during all times during the connection, the physical path used for the transmission cannot be used for any other purpose, such as use by other users. Circuit-switched networks may be contrasted with packet-switched networks.
Packet-switched describes a type of network in which relatively small units of data called packets are routed through a network based on a destination address contained within each packet. Breaking communications down into discrete packets allows the same data path to be shared during a given time interval by multiple users in the network.
Higher efficiency transmission of data over cellular networks has been accomplished by transmitting data in a packetized format over vacant voice channels. Voice channels are generally vacant during approximately 50% of each call, since participants in a conversation generally take turns talking. One variant of packet data transmission is called Cellular Digital Packet Data (CDPD).
CDPD is a specification for supporting wireless access to the Internet and other public packet-switched networks. Cellular telephone and modem providers that offer CDPD make it possible for mobile users to get access to the Internet at theoretical data rates of up to 19.2 Kbps. Because CDPD is an open specification that adheres to the layered structure of the Open Systems Interconnection (OSI) model, it has the ability to be extendable into the future. CDPD supports both the Internet's IP protocol and the ISO Connectionless Network Protocol (CLNP). There is also a circuit-switched version of CDPD, called CS CDPD, which can generally only be used to improve system efficiently when traffic is expected to be heavy enough to warrant a dedicated connection.
CDPD has been implemented in analog cellular networks such as the Advanced Mobile Phone System (AMPS) in U.S. Pat. No. 5,404,392 to Miller et al. CDPD has also been implemented in digital cellular time division multi-access (TDMA) networks in U.S. Pat. No. 5,790,551 to Chan.
Some cellular systems use repeaters, such as translating repeaters, to lower the cost per channel in relatively low cellular usage zones. Some translating repeaters, such as the AirSite® repeater system offered by AirNet Communications Corporation of Melbourne, Fla., make use of existing “in-band” RF carrier frequencies for backhaul cellular communications traffic. As used herein, the term “in-band” refers to carrier frequencies that are within the frequency spectrum allocation assigned to the service provider for providing cellular communications services to mobile subscribers. Use of in-band radio frequency channels for backhaul cellular communications traffic from remote translating repeater sites eliminates costly wireline T1 or microwave connections.
While the use of in-band radio frequency channels for backhaul cellular communications traffic has distinct advantages, it also has some drawbacks. For example, in conventional wireless translating repeaters, a full duplex backhaul channel requires a pair of corresponding uplink and downlink backhaul RF carrier frequencies. Use of such in-band channels for providing a backhaul link necessarily reduces the number of channels available to a service provider on which to communicate with mobile subscribers. As mobile subscriber traffic increases, additional RF carrier channels must be allocated for the backhaul function. Thus, since there are a finite number of RF channels that can be allocated for use as backhaul channels and a finite number of RF channels that can be allocated as groundlink channels, the number of translating repeaters and mobile subscribers that may be supported by a given cellular network is correspondingly limited.
Exclusive assignment of backhaul frequencies results from currently used circuit switched technology for the backhaul. Using circuit switched technology, calls received by the translating repeater from a mobile user and re-transmitted on the uplink to the base transceiver station (BTS) requires the allocation, by the BTS, of at least a portion of the bandwidth of the backhaul channel. The allocation is an exclusive allocation for the entire duration of the call.
Thus, while information is being sent from the mobile user to the translating repeater and from the translating repeater to the BTS, the bandwidth of the downlink backhaul channel remains exclusively allocated to the recipient of the call for transmitting information of their own to the mobile user. This is the case even though while the mobile user is talking to the call recipient, the call recipient is generally merely listening to the information received from the mobile user. Similarly, the uplink backhaul channel remains allocated and unavailable for other users as it sits idle while the call recipient is talking to the mobile user.
In the case of voice networks, information is only transmitted along the allocated bandwidth of a given voice channel about 50% of the time. Accordingly, the efficiency of cellular systems having translating repeaters could be substantially improved if data could be transmitted by another translating repeater served by a given host BTS during time intervals when the allocated backhaul bandwidth of an initiated cellular call was not being used. This would allow the efficiency of transmissions of voice and other information over the backhaul channel to be greatly increased. This efficiency increase is expected to be on the order of approximately 200%, or approximately twice the effective backhaul network traffic capacity compared to a circuit switched backhaul network. Similar efficiencies may also be realized on the downlink backhaul channel using the same method. Backhaul efficiencies could be further increased if use of vacant voice channel intervals could be combined with other compatible techniques which also improve backhaul channel efficiency.